10,439 research outputs found
Ultrasensitive and Wide-Bandwidth Thermal Measurements of Graphene at Low Temperatures
Graphene is a material with remarkable electronic properties[1] and exceptional thermal transport
properties near room temperature, which have been well examined and understood[2, 3].
However at very low temperatures the thermodynamic and thermal transport properties are much
less well explored[4, 5] and somewhat surprisingly, is expected to exhibit extreme thermal isolation.
Here we demonstrate an ultra-sensitive, wide-bandwidth measurement scheme to probe the
thermal transport and thermodynamic properties of the electron gas of graphene. We employ
Johnson noise thermometry at microwave frequency to sensitively measure the temperature of the
electron gas with resolution of 4mK/√Hz and a bandwidth of 80 MHz. We have measured the
electron-phonon coupling from 2-30 K at a charge density of 2 •10^(11)cm^(-2). Utilizing bolometric
mixing, we have sensed temperature oscillations with period of 430 ps and have determined the
heat capacity of the electron gas to be 2 • 10^(-21)J/(K •µm^2) at 5 K which is consistent with that
of a two dimensional, Dirac electron gas. These measurements suggest that graphene-based devices
together with wide bandwidth noise thermometry can generate substantial advances in the
areas of ultra-sensitive bolometry[6], calorimetry[7], microwave and terahertz photo-detection[8],
and bolometric mixing for applications in areas such as observational astronomy[9] and quantum
information and measurement[10]
Program to develop sprayed, plastically deformable compressor shroud seal materials
A study of fundamental rub behavior for ten dense sprayed materials and eight current compressor clearance materials has been conducted. A literature survey of a wide variety of metallurgical and thermophysical properties was conducted and correlated to rub behavior. Based on these results, the most promising dense rub material was Cu-9Al. Additional studies on the effects of porosity, incursion rate, blade solidity and ambient temperature were carried out on aluminum bronze (Cu-9Al-1Fe) with and without a 515B Feltmetal underlayer
On localization effects in underdoped cuprates
We comment on transport experiments in underdoped LaSrCuO in the
non-superconducting phase. The temperature dependence of the resistance
strongly resembles what is expected from standard localization theory. However
this theory fails, when comparing with experiments in more detail.Comment: 8 pages, to be published in J. of Superconductivit
Superfluid Optomechanics: Coupling of a Superfluid to a Superconducting Condensate
We investigate the low loss acoustic motion of superfluid He
parametrically coupled to a very low loss, superconducting Nb, TE
microwave resonator, forming a gram-scale, sideband resolved, optomechanical
system. We demonstrate the detection of a series of acoustic modes with quality
factors as high as . At higher temperatures, the lowest
dissipation modes are limited by an intrinsic three phonon process. Acoustic
quality factors approaching may be possible in isotopically purified
samples at temperatures below 10 mK. A system of this type may be utilized to
study macroscopic quantized motion and as an ultra-sensitive sensor of
extremely weak displacements and forces, such as continuous gravity wave
sources
Putting mechanics into quantum mechanics
Nanoelectromechanical structures are starting to approach the ultimate quantum mechanical limits for detecting and exciting motion at the nanoscale. Nonclassical states of a mechanical resonator are also on the horizon
Onsager relations in a two-dimensional electron gas with spin-orbit coupling
Theory predicts for the two-dimensional electrons gas with only Rashba
spin-orbit interaction a vanishing spin Hall conductivity and at the same time
a finite inverse spin Hall effect. We show how these seemingly contradictory
results are compatible with the Onsager relations: the latter do hold for spin
and particle (charge) currents in the two-dimensional electron gas, although
(i) their form depends on the experimental setup and (ii) a vanishing bulk spin
Hall conductivity does not necessarily imply a vanishing spin Hall effect. We
also discuss the situation in which extrinsic spin orbit from impurities is
present and the bulk spin Hall conductivity can be different from zero.Comment: Accepted versio
Ultra-high Q Acoustic Resonance in Superfluid 4He
We report the measurement of the acoustic quality factor of a gram-scale,
kilo-hertz frequency superfluid resonator, detected through the parametric
coupling to a superconducting niobium microwave cavity. For temperature between
400mK and 50mK, we observe a temperature dependence of the quality
factor, consistent with a 3-phonon dissipation mechanism. We observe Q factors
up to , consistent with the dissipation due to dilute He
impurities, and expect that significant further improvements are possible.
These experiments are relevant to exploring quantum behavior and decoherence of
massive macroscopic objects, the laboratory detection of continuous wave
gravitational waves from pulsars, and the probing of possible limits to
physical length scales.Comment: 5 pages, 2 figure
Non-linear conductivity and quantum interference in disordered metals
We report on a novel non-linear electric field effect in the conductivity of
disordered conductors. We find that an electric field gives rise to dephasing
in the particle-hole channel, which depresses the interference effects due to
disorder and interaction and leads to a non-linear conductivity. This
non-linear effect introduces a field dependent temperature scale and
provides a microscopic mechanism for electric field scaling at the
metal-insulator transition. We also study the magnetic field dependence of the
non-linear conductivity and suggest possible ways to experimentally verify our
predictions. These effects offer a new probe to test the role of quantum
interference at the metal-insulator transition in disordered conductors.Comment: 5 pages, 3 figure
Three-dimensional elliptic grid generation technique with application to turbomachinery cascades
Described is a numerical method for generating 3-D grids for turbomachinery computational fluid dynamic codes. The basic method is general and involves the solution of a quasi-linear elliptic partial differential equation via pointwise relaxation with a local relaxation factor. It allows specification of the grid point distribution on the boundary surfaces, the grid spacing off the boundary surfaces, and the grid orthogonality at the boundary surfaces. A geometry preprocessor constructs the grid point distributions on the boundary surfaces for general turbomachinery cascades. Representative results are shown for a C-grid and an H-grid for a turbine rotor. Two appendices serve as user's manuals for the basic solver and the geometry preprocessor
Mesoscopic Mechanical Resonators as Quantum Non-Inertial Reference Frames
An atom attached to a micrometer-scale wire that is vibrating at a frequency
of 100 MHz and with displacement amplitude 1 nm experiences an acceleration
magnitude 10^9 ms^-2, approaching the surface gravity of a neutron star. As one
application of such extreme non-inertial forces in a mesoscopic setting, we
consider a model two-path atom interferometer with one path consisting of the
100 MHz vibrating wire atom guide. The vibrating wire guide serves as a
non-inertial reference frame and induces an in principle measurable phase shift
in the wave function of an atom traversing the wire frame. We furthermore
consider the effect on the two-path atom wave interference when the vibrating
wire is modeled as a quantum object, hence functioning as a quantum
non-inertial reference frame. We outline a possible realization of the
vibrating wire, atom interferometer using a superfluid helium quantum
interference setup.Comment: Published versio
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